As I’ve written before, the hardest part of landscape photography is retaining detail in a bright sky with a darker foreground. There are several ways to deal with this issue. The newest ways involve various post-processing techniques in Photoshop or Lightroom, or using High Dynamic Range photography to blend several exposures together, retaining both shadow and highlight detail from these exposures. There is nothing wrong with these techniques, and in fact there are times where these may be the best method for keeping detail in the sky. There are issues with both blending and HDR. HDR tends to have a very processed look to it when not done well, and blending takes time to do well. I am not one who likes to spend much time in Photoshop with my images. In addition, you still need to be sure that you somehow capture enough information in the sky that you are not simply darkening down white pixels.
To ensure you’re capturing enough detail, the use of graduated neutral density filters is needed. Graduated Neutral Density Filters (ND grads, for short), are pieces of glass or photographic resin that are half clear, and gradually gets darker as it moves to the other end. This darkening begins in the middle of the piece of glass. First of all, these filters come in two forms. The first of which is a typical screw-on filter that screws onto the front of the lens. While this style is fine for polarizers or skylight filters, it’s problematic for ND grads, because the horizon can’t be repositioned. The other way these filters come is in 4×5 or 4×6 inch glass or resin. These pieces of glass are then placed in holders, and the horizon can be repositioned as needed. The biggest advantage these filters have over the screw-in kind is the fact that they allow you freedom of composition to put the horizon where you want. The most popular holders and systems for this type of filter are the Cokin systems, which come in various sizes, and the Lee system, which typically accepts a 4″ wide filter. The Cokin systems tend to be a bit cheaper both in terms of cost of the holder and cost of the filters. The Lee system is a bit more expensive on both fronts.
Once you’ve decided on which system to use, there is then the choice of which ND grads to choose. There are several companies that manufacture these filters, from Cokin for their systems, to Lee, to to Formatt Hi Tech, to Schneider Optics, among others. The prices vary, depending on whether you’re buying photographic resin or glass. Resin filters tend to be cheaper while glass is most expensive. Resin doesn’t break when dropped but can scratch more easily than glass does. ND grads are available in various densities, including 2 stops, 3 stops, and 4 stops.
The selection doesn’t stop there, however. In addition to choosing which density you need, you also must choose how gradual the density is. Graduated neutral density filters come in both hard-edge and soft-edge graduations. You would use hard-edge filters when you have a clear horizon and no object in the foreground intersects it. You would use soft-edged filters when there is an object that intersects the horizon. Soft-edge filters have a much smoother gradation, which allows it to look more natural when used in a photo. A hard-edged filter will create a more definitive line between light and dark in the image.
These filters have become some of the most important tools in my bag when creating landscape photos. If you’re just starting out, get an inexpensive set of filters- there is no “one size fits all” to ND grads. However, if you can only start with one, I’d suggest a soft-edged three stop ND grad. The hard-edged can be limiting at times, and two stops never seems to be enough on its own. I often stack ND grads to get the effect I’m looking for.